In the related art, a sewing system has been developed in which a front end portion of a robot arm is equipped with a sewing machine and sewing is performed on a curved surface which is three-dimensionally shaped without the sewing being limited to a flat surface.
When sewing begins in this sewing system, if a needle center position of the sewing machine which is set in a coordinate system of the robot arm, and an actual needle center position of the assembled sewing machine are not precisely consistent with each other, the sewing as desired cannot be performed, and an improvement in sewing quality cannot be achieved (for example, refer to JP-A-H05-305193).
The needle center position of the sewing machine which is set in the coordinate system of the robot arm and the actual needle center position of the sewing machine are precisely consistent with each other if the sewing machine is precisely assembled to the robot arm, but this requires high precision for assembling work of the sewing machine and causes a problem that the burden of the assembling work becomes very large.